(a) Technical Field
The present invention relates to a carbon nanomaterial pellet and a method for preparing same. More particularly, it relates to a carbon nanomaterial pellet having a specific size and a high apparent density prepared by a simple process using only a rotary tablet press without mixing a carbon nanomaterial powder with a solvent or an additive, which is capable of solving the powder dust problem occurring when preparing a polymer composite from a carbon nanomaterial in the form of powder, thus improving physical properties and remarkably reducing cost of packaging and transportation, and a method for preparing the carbon nanomaterial pellet from a carbon nanomaterial powder.
(b) Background Art
Carbon nanomaterials include fullerene, carbon nanotube (CNT), graphene, graphite nanoplate, etc. Among them, a carbon nanotube has a cylindrical nanostructure with a honeycomb-shaped sheet of graphite rolled to a diameter of nanometer scale and has specific characteristics depending on shape. The carbon nanotube is light since it has a hollow space, has good electrical conductivity comparable to that of copper, has good thermal conductivity comparable to that of diamond and has good tensile strength comparable to that of steel. It is also categorized as single-walled carbon nanotube (SWCNT), multi-walled carbon nanotube (MWCNT) or rope carbon nanotube according to the rolling type.
Owing to its superior physical properties, the carbon nanotube is drawing attentions as filler of various polymer composites, including antistatic polymer composites, EMI-shielding polymer composites, heat-resistant polymer composites, high-strength polymer composites, and so forth. Many researches and developments are underway for commercialization of polymer composites using the carbon nanotube.
However, despite the R&D efforts, the dust problem due to low apparent density of carbon nanotube powder and health issue arising therefrom remain as obstacles to the use of the carbon nanotube in polymer composites.
In general, the nanomaterial such as the carbon nanotube is used as mixed with a polymer pellet. When carbon nanomaterial powder is supplied to an extruder together with the polymer pellet, layer separation due to the large density difference of the carbon nanomaterial powder and the polymer pellet and dispersion problem of the carbon nanomaterial as a result thereof make large-scale use of the carbon nanomaterial difficult. Besides, in view of carbon nanomaterial producers, the very low apparent density of the carbon nanomaterial produced in the form of powder is the cause of increased cost of packaging and transportation.
Methods for improving apparent density of carbon nanomaterials, especially carbon nanotube, disclosed in the published patents include the followings.
Korean Patent No. 10-0955295 titled “Manufacturing method of shaped solid comprising nanocarbon” discloses a shaped solid comprising a nanocarbon, a metal (including oxide and ion) and a resin. However, since the prepared shaped solid comprises the metal and the resin to enhance binding for shaping the solid, when it is used in a polymer composite, a polymer used as a matrix may react with or be incompatible with the metal and the resin included in the solid, resulting in degradation of important physical properties of the nanocarbon. In addition, the method requires several steps of mixing of the nanocarbon with the metal and the resin, separation, shaping and drying.
Korean Patent Publication No. 2011-0065704 titled “Manufacturing method of nanocarbon shaped body and manufacturing method of nanocarbon shaped body, nanocarbon dispersed solution and nanocarbon material using same” discloses a method for manufacturing a nanocarbon shaped body comprising cutting a nanocarbon, mixing the nanocarbon with a dispersant and a solvent and dispersing the nanocarbon using a dispersing apparatus, flocculating the nanocarbon dispersed solution into a nanocarbon sludge by further adding a coagulant, removing a liquid component from the nanocarbon sludge and crushing or pulverizing same into a nanocarbon powder, and shaping the nanocarbon powder and drying same to prepare a nanocarbon shaped body. However, this method has a problem in that, although a metal or a resin is not included in the nanocarbon shaped body, the dispersant and the coagulant used during the manufacture may remain in the nanocarbon shaped body and cause unexpected negative effects when it is used to prepare a polymer composite. Further, the method also requires several steps.
Korean Patent Publication No. 2010-0038094 titled “Granulated product of carbon nanotube and method for production thereof”, filed by Mikuni Shikiso Kabushiki Kaisha, discloses a method for producing a granulated product of a carbon nanotube wherein a carbon nanotube is granulated using a gas/liquid or liquid/liquid interface, using the carbon nanotube and a solvent at a weight ratio of at least 1:3. Although the apparent density of the carbon nanotube is increased by this method, the dust problem cannot be solved completely since fine carbon nanotube powder is included in the granulated product. Also, the method is not appropriate for large-scale production since mixing, degasing and drying steps are involved in the manufacturing process.